Well - it means exactly what it says... DBD::Sybase (and all Sybase related products) use the $SYBASE environment variable to determine where things are installed (libraries, locale files, charset files, etc). You need to set $SYBASE before running "perl Makefile.PL" (or edit the CONFIG file and set it there.)

On a Sybase 12.x system (Unix/linux) the easiest way to set all the appropriate environment variables is to source the SYBASE.sh or SYBASE.csh file located in the root directory of the Sybase installation.

Michael